Method for Driving Quad-Subpixel Display

1. A method of displaying an image on a display, comprising: receiving a display signal that defines an image, wherein a display color gamut is defined by three sets of CIE coordinates (x RI , y RI ), (x GI , y GI ), (x sI , y BI ) the display signal is defined for a plurality of pixels; for each pixel, the display signal comprises a desired chromaticity and luminance defined by three components R I , G I and B I that correspond to luminances for three sub-pixels having CIE coordinates (x RI , y RII ), (x GI , y GI ) and (x BI , y BI ), respectively, that render the desired chromaticity and luminance; wherein the display comprises a plurality of pixels, each pixel including an R sub-pixel, a G sub-pixel, a B1 sub-pixel and a B2 sub-pixel, wherein: each R sub-pixel comprises a first organic light emitting device that emits light having a peak wavelength in the visible spectrum of 580-700 mu, further comprising a first emissive layer having a first emitting material; each G sub-pixel comprises a second organic light emitting device that emits light having a peak wavelength in the visible spectrum of 500-580 nm, further comprising a second emissive layer having a second emitting material; each B1 sub-pixel comprises a third organic light emitting device that emits light having a peak wavelength in the visible spectram of 400-500 nm, further comprising a third emissive layer having a third emitting material; each B2 sub-pixel comprises a fourth organic light emitting device that emits light having a peak wavelength in the visible spectrum of 400 to 500 nm, further comprising a fourth emissive layer having a fourth emitting material; the third emitting material is different from the fourth emitting material; and the peak wavelength in the visible spectrum of light emitted by the fourth organic light emitting device is at least 4 nm less than the peak wavelength in the visible spectrum of light emitted by the third organic light emitting device; wherein each of the R, G, B1 and B2 sub-pixels has CIE coordinates (x R , y R ), (x G , y G ), (x B1 , y B1 ) and (x B2 , y B2 ), respectively; wherein each of the R, G, B1 and B2 sub-pixels has a maximum luminance Y R , Y G , Y B1 and Y B2 , respectively, and a signal component R C , G C B1 C and B2 C , respectively; wherein a plurality of color-spaces are defined, each color space being defined by the CIE coordinates of three of the R, G, B1 and B2 sub-pixels, wherein every chromaticity of the display gamut is located within at least one of the plurality of color spaces; wherein at least one of the color spaces is defined by the R, G and B2 sub-pixels; wherein the color spaces are calibrated by using a calibration chromaticity and luminance having a CIE coordinate (x C , y C ) located in the color space defined by the R, B and B1 sub-pixels, such that: a single maximum luminance for the display is defined for each of the R, G, B1 and B2 sub-pixels, for each color space, for chromaticities located within the color space, a linear transformation is defined that transforms the three components R I , G I and B I into luminances for the each of the three sub-pixels having CIE coordinates that define the color space that will render the desired chromaticity and luminance defined by the three components R 1 , G 1 and B 1 ; displaying the image by, for each pixel: choosing one of the plurality of color spaces that includes the desired chromaticity of the pixel; transforming the R I , G I and B I components of the signal for the pixel into luminances defined relative to the maximum luminance for the display for each of the three sub-pixels having CIE coordinates that define the chosen color space; emitting light from the pixel having the desired chromaticity and luminance using the luminances resulting from the transformation of the R I , G I and B I components.

2. The method of claim 1 , wherein: two color spaces are defined: a first color space defined by the CIE coordinates of the R, G and B1 sub-pixels, and a second color space defined by the CIE coordinates of the R, G and B2 sub-pixels.

3. The method of claim 2 , wherein: the first color space is chosen for pixels having a desired chromaticity located within the first color space; and the second color space is chosen for pixels having a desired chromaticity located within a subset of the second color space defined by the R, B1 and B2 sub-pixels.

4. The method of claim 3 , wherein the color spaces are calibrated by using a calibration chromaticity and luminance having a CIE coordinate (x C , Y C ) located in the color space defined by the R, G and B1 sub-pixels by: defining maximum luminances (Y′ R , Y′ G and Y′ B1 ) for the color space defined by the R, G and B1 sub-pixels, such that emitting luminances Y′ R , Y′ G and Y′ B 1 from the R, G and B1 sub-pixels, respectively, renders the calibration chromaticity and luminance; defining maximum luminances (Y″ R , Y″ G and Y B2 ) for the color space defined by the R, G and B2 sub-pixels, such that emitting luminances Y″ R , Y″ G and Y″ 52 from the R, G and B2 sub-pixels, respectively, renders the calibration chromaticity and luminance; defining maximum luminances (Y R , Y G , Y B1 and Y B2 ) for the display, such that Y R =max (Y R ′, Y R ″), Y′ G =max (Y G ′, Y G ″), Y B1 =Y′ B1 , and Y B2 =Y′ R2 .

5. The method of claim 4 , wherein: the linear transformation for the first color space is a sealing that transforms R I into R C , G I into G C , and B I into B1 C ; and the linear transformation for the second color space is a scaling that transforms R I into R C , G I into G C , and B I into B2 C .

6. The method of claim 2 , wherein the CIE coordinates of the B1 sub-pixel are located outside the second color space.

7. The method of claim 1 , wherein: two color spaces are defined: a first color space defined by the CIE coordinates of the R, G and B1 sub-pixels, and a second color space defined by the CIE coordinates of the R, B1 and B2 sub pixels.

8. The method of claim 7 , wherein: the first color space is chosen for pixels having a desired Chromaticity located within the first color space; and the second color space is chosen for pixels having a desired chromaticity located within the second color space.

9. The method of claim 7 , wherein the CIE coordinates of the B1 sub-pixel are located outside the second color space.

10. The method of claim 1 , wherein: the CIE coordinates of the B1 sub-pixel are located inside a color space defined by the CIE coordinates of the R, G and B2 sub-pixels; three color spaces are defined: a first color space defined by the CIE coordinates of the R, G and B1 sub-pixels; a second color space defined by the CIE coordinates of the B2 and B1 sub-pixels; and a third color space defined by the CIE coordinates of the B2, R and B1 sub-pixels.

11. The method of claim 10 , wherein: the first color space is chosen for pixels having a desired chromaticity located within the first color space; and the second color space is chosen for pixels having a desired chromaticity located within the second color space; and the third color space is chosen for pixels having a desired chromaticity located within the third color space.

12. The method of claim 1 , wherein the CIE coordinates are 1931 CIE coordinates.

13. The method of claim 1 , wherein the calibration color has a CIE coordinate (x C , y C ) such that 0.25<x C <0.4 and 0.25<y C <0.4.

14. The method of claim 1 , wherein the CIE coordinate of the B1 sub-pixel is located outside the triangle defined by the R, G and B2 CIE coordinates.

15. The method of claim 1 , wherein the CIE coordinate of the B1 sub-pixel is located inside the triangle defined by the R, G and B2 CIE coordinates.

16. The method of claim 1 , wherein the first, second and third emitting materials are phosphorescent emissive materials, and the fourth emitting material is a fluorescent emitting material.